Apparatus for liquefying air



Oct. 2, 1956 J. w. L. KGHLER 2,754,877

APPARATUS FOR LIQUEFYING AIR Filed March 23, 1951 2 Sheets-Sheet l w 14If caZ G JACOB w. L. KOHLER INl/E/VT'OR AGE/VT Oct. 2, 1956 Filed March23, 1951 2 Sheets-Sheet 2 IN VEN TOR. JACOB WILLEM LAURENS KOHLER AGENTUnited States 2,764,877 APPARATUS FOR LIQUEFYING AIR Jacob WillemLaurens Kiihler, Eindhoven, Netherlands,

assignor to Hartford National Bank and Trust Company, Hartford, Conn.,as trustee This invention relates to methods of cooling gases to atemperature comprised in the co-existence range of the gas to be cooled,so that at least part of the gas becomes liquid.

The object of the present invention is to provide a method by which agas can be cooled to a temperature comprised in the co-existence rangeof the gas to be cooled, the output of the installation being many timeshigher than that of the systems described above, the installation itselfhaving a small volume compared with known installations.

According to the invention, a quantity of compressed gas is cooled,after which this cooled gas is cooled further by means of the coldproduced by the cold-gas cooling machine operating on the reversedhot-gas reciprocating engine principle, liquid being thus formed, afterwhich the medium produced during the last-mentioned cooling processundergoes a decrease in pressure, the first-mentioned cooling processbeing carried out with the use of cold from the gas cooled by thismethod.

The term cold-gas cooling machine operating on the reversed hot-gasengine principle is to be understood here to mean a machine in whichmechanical energy is converted into thermal energy and in which a mediumof invariable chemical composition, which is constantly in the gaseousphase, traverses an open or closed thermodynamic cycle in at least twointercommunicating chambers or chamber parts of ditferent temperatures,expansion of this medium primarily taking place in one or in a few ofthese chambers or chamber parts and compression in one or a few of theother chambers or chamber parts respectively, said machine comprisingmeans to carry off heat to the exterior during compression and/or tosupply heat from the exterior during expansion.

The medium produced during the cooling by the coldgas cooling machinemay be either exclusively liquid or a mixture of gas and liquid.

In a further method according to the invention, which is used to liquefygases, a quantity of compressed gas is cooled by a smaller quantity ofthis gas flowing back and having a lower pressure, after which thiscooled gas is cooled further by means of the cold produced by a coldgascooling machine operating on the reversed hotgas reciprocating engineprinciple, liquid being thus formed, whereafter the medium producedduring the last-mentioned cooling process undergoes a decrease inpressure, the residual gas performing the first-mentioned cooling of thecompressed gas.

atent C In a further method according to the invention, which I is usedto disintegrate gases into constituents, a quantity of compressed gaswhich is to be distinguished is cooled by a quantity of gas flowing backafter which this cooled gas is cooled further by means of the cold-gascooling machine, liquid being thus formed, whereafter the mediumproduced during the latter cooling process undergoes a decrease inpressure and is separated into the desired constituents, at least one ofthe constituents performing the first-mentioned cooling of the gas to bedisintegrated into constituents.

In a further method according to the invention, the medium after it hasbeen formed by means of the cold produced by the cold-gas coolingmachine, is cooled further with the use of cold obtained from the gascooled by a method according to the invention, while the cooling of thecompressed gas, before being cooled with the use of the cold-gascoolingmachine, is likewise performed by means of cold obtained from the cooledgas.

By carrying out this method, the percentage of liquefied gas can beincreased further. I I

In a preferred embodiment of the method, the pressure of the compressedgas is not more than the critical pressure of this gas. In the case ofair, this means that the gas need be compressed to at most 40atmospheres Since in the known installations described above, the gas iscompressed to,'for example, 200 atmospheres, it will be evident that,owing to the low compression utilized in accordance with the invention,a material simplification of the installation is obtainable.

The invention may be successfully used more particularly if thecompressed gas is cooled by means of the cold-gas cooling machine to atemperature located in the neighborhood of the point of intersection ofthe pressure line of this gas and the liquid limiting line of thecoexistence range. This means that the compressed gas has becomecompletely liquid, after it has been cooled with the use of the cold-gascooling machine. If thereupon the liquid gas is caused to expand to 1atmosphere, a new quantity of gas will be produced, it is true, but thequantity of liquid will nevertheless be comparatively large.

In a further preferred embodiment of the method according to theinvention, cold is abstracted from the working medium in the cold-gascooling machine with the use of cold obtained from the cooled gas.

The installation adapted for carrying out the method described above hasthe feature that it comprises a heatexchanger in which the compressedgas is cooled, a coldgas cooling machine with the use of which this gasis cooled further, liquid being thus produced, and a device in whichthereupon the pressure and, if desired, the temperature of the mediumare decreased.

The device in which the pressure and, if necessary, the temperature ofthe gas are decreased, may be constituted by -a choking device, out ofwhich the liquid drops at a pressure of, for example, 1 atmosphere.However, as an alternative, this device may be constituted by a tubularcooler, through which the medium is led. This tubular cooler is arrangedin the container with the boiling liquid. The liquid cooling the medium,which may be either a liquid or a mixture of liquid and gas, startsboiling in the container owing to the heat supplied to the liquid fromthe tubular cooler.

According to a further embodiment of the invention, the medium, after ithas been produced by means of a cold-gas cooling machine, is cooled in aheat exchanger. Thus, the percentage of liquefied gas may be increased.In installations for liquefying gases that portion of the gas which isfinally not liquefied will serve as the cooling medium for this heatexchanger. In fractionating installations, it will be advantageous forone or more of the constituents into which the gas is disintegrated toserve as the cooling medium. In certain cases it may be advantageousalso to lead the gas which is finally not liquefied, or the constituentsof the gas, along that heat-exchanger of the cold-gas cooling machine inwhich heat is abstracted from the working medium in the machine.

When a gas containing admixtures is to be liquefied or fractionated intoconstituents, these admixtures becomnig liquid or solid at a highertemperature than the gas to be finally liquefied, itis desirable thatthe admixtures should preliminarily be removed from the gas. Such a casewill, for example, occur when nitrogen and oxygen are to be liquefiedfrom the air. Apart from nitrogen and oxygen, the air comprisesadditionally water vapour and carbon dioxide. It is not desirable thatthese constituents should deposit themselves in a normal heat-exchanger,which may be, for example, a tubular cooler. The constituents may beextracted from the gas by chemical washing of the gas.

In a further embodiment of the invention, the first heatexchanger, inwhich the compressed gas is cooled, is constituted by a reversibleregenerator or recuperator system. The constituents of the gas liable tobe deposited in this heat-exchanger may thus be periodically removed.The change-over of the regenerator or recuperator system may beperformed continuously or periodically. By the use of this heatexchanger, the installation may be materially simplified.

This heat-exchanger may be successfully used more particularly if thequantity of gas, which flows back and which gives or cold to thecompressed gas is large. This will generally be the case, if theinstallation is used for fractionating gases. According to oneembodiment of the invention, this installation has the feature that themedium, after it has been subjected to its last cooling process, isfractionated into constituents in a fractionating apparatus.

In order that the invention may be readily carried into effect, twoexamples will now be described in detail with reference to theaccompanying drawings, of which:

Fig. 1 is a diagrammatical view of an installation for use with themethod according to the invention;

Fig. 2 shows the W-T diagram of this method and Fig. 3 is a diagrammaticview of a fractionatinginstallation according to the invention,

Pig. 4 is a partially perspective view of a cold-gas cooling machine inaccordance with the present invention.

Referring to the diagrammatic view of Fig. 1, a quantity of air iscompressed to 20 atmospheres in a compressor 1. Then, this quantity ofair is cooled under a constant pressure in a first heat-exchanger 2, forexample, to 223 Kelvin. It enters into the heat-exchanger at and leavesit at 11. The cooling medium is constituted by that portion of the gaswhich has finally not been liquefied. Then, the gas cooled to 223 Kelvinflows along the cold side 3 of a cold-gas cooling machine 4, which isdriven by an electric motor. This cold-gas cooling machine operates onthe reversed hot-gas engine principle. Apart from the embodimentindicated above, in which the gas to be cooled flows directly throughthe heat-exchanger on the cold side of the cooling machine, it will incertain cases be desirable that the cooling of the gas should not beperformed directly by the cooling machine, but with the use of anintermediate medium. After the gas has been cooled with the use of thecold-gas cooling machine, it will have become completely liquid. In thiscase the temperature may, for example, be 108 Kelvin. Then, the liquidis cooled further, for example, to 105 Kelvin, in a heat-exchanger 5.The liquid enters into the heat exchanger at 12 and leaves it at 13.Finally, with the use of a choking device 6, the pressure of the mixtureof liquid and gas may be reduced from 20 atmospheres to 1 atmosphere.The liquid dripping from the choking device 6 is collected in acontainer 7.

That portion of the gas which has finally not become liquid, first flowsthrough the heat exchanger 5, giving off part of its cold to the liquidwhich is formed with the use of the cooling machine. The gas flowsthrough the heat exchanger 2, in which it gives off the remainder of itscold to the compressed gas. With a correct construction of thisheat-exchanger, the temperature of the gas of low pressure, when itleaves the heat exchanger, and the temperature of the gas of highpressure, when it enters the heat-exchanger, may be substantially equal.After adding a new quantity of gas which is supplied at 8, the expandedgas may be recompressed in the compressor 1, after which it can repeatits cycle. It is thus ensured that less water and carbonic acid have tobe extracted from the air than if the gas did not repeat its cycle.

Fig. 2 shows the W-T diagram for air. The temperature in degrees Kelvinis plotted on the abscissa of the diagram, the heat content of the airper kilogram being plotted on the ordinate. The compressed air of 20atmospheres enters the first heat-exchanger 2 at point 10: here the airis cooled to point 11, where it leaves the heatexchanger. At thistemperature of 223 Kelvin, it is cooled with the use of the cold-gascooling machine. This cooling is performed at constant pressure, so thatthe pressure line of 20 atmospheres is followed. The cooling continuesuntil point 12 on the liquid limiting line of the co-existence range isreached. Then, with the use of the heat exchanger 5, the gas is cooledfurther to point 13 which lies lower on the liquid limiting line of thecoexistence range. The pressure of the liquid is reduced to 1 atmospherein the choking device 6. This decrease in pressure is indicated in thediagram as a horizontal line. The final condition of the mixture of gasand liquid is indicated at 14. It is evident from the diagram that morethan 60% of the initially compressed gas has been liquefied.

Fig. 3 shows diagrammatically a device in which the method according tothe invention is carried out to fractionate gases. The device roughlycorresponds to that shown in Fig. 1.

Referring to Fig. 3, a quantity of air is compressed to, for example, 20atmospheres in a compressor 31. Then, this air is cooled in aheat-exchanger 32. This cooling may, for example, be performed to 223Kelvin. Then, with the use of the cold supplied by a cold-gas coolingmachine 33, which is driven by an electric motor, the air is cooledfurther to, for example, 108 Kelvin, the air then having become liquid.The liquid air is cooled further in a heat-exchanger 34. Then, theliquid air enters into a fractionating column 36 at 35. The container 37of the fractionating column contains a quantity of liquid oxygen, whichhas a temperature lower than that of the liquid air, which is ledthrough a tubular cooler 38 into the container. Owing to the supply ofheat from the liquid air, the oxygen keeps boiling. The liquid airleaves the tubular cooler 38 of the fractionating column at 39, passesthrough a choking cock 40 and enters, at a pressure of, for example, 1atmosphere into the upper part of the fractionating column at 41. Theliquid air drips down along tiles 42. The gas is separated into oxygenand nitrogen in a column 43, the nitrogen and oxygen leaving the columnat 44 and 45 respectively. The nitrogen and the oxygen are each ledthrough different tubular coolers across the heat-exchanger 34, in whichthe components give off cold to the gas to be fractionated, passingsubsequently through the heat-exchanger 32, in which cold is also givenoff to the gas to be fractionated. After the two gases have left theheat-exchanger 32, which is preferably constituted by a reversibleregenerator or recuperator system, the two constituents can be storedseparately in cylinders.

Fig. 4 shows on a different scale a cold-gas refrigerator suitable foruse in the systems described above. The cold-gas refrigerator shown isof the socalled displacerpiston type. Of course, use may be made ofother types of cold-gas refrigerators, for example, double-actingmachines.

The machine comprises a cylinder 60, in which 'a displacer piston 61 anda piston 62 are adapted to reciprocate with a substantially constantphase difference. To this end the displacer piston is coupled by meansof a connecting rod mechanism 63 with a crank of a crank shaft 64, whilethe piston 62 is coupled by way of a connectingrod system 55 with twocranks of the same crank shaft 64. Owing to the movement of thedisplacer piston 61 the volume of the freezing space 66 is varied. Thisspace communicates with the cooled space 70 through a freezer 67, aregenerator 68 and a cooler 69; the volume of the cooled space is variedboth by the movement of the dis placer piston 61 and the movement of thepiston 62.

The refrigerator is driven by an electric motor 71. Cold-gasrefrigerators permits the obtaining in one stage of low temperatures offor example 200 C.

A medium to be cooled may be supplied through ports 72 to a space 73,which is surrounded by a jacket 74 having heat insulating properties. Inthis space 73 the medium is cooled, after which the cooled medium leavesthe refrigerator through a duct 75.

In the embodiments of the invention described above, use is made of acold-gas cooling machine, in which the required temperature (starting,for example, at room temperature) is reached in a single step.Particularly if the gas to be liquefied, upon leaving theheat-exchangers in which it is cooled with the use of the cold-gascooling machine, has a very low temperature, it is advisable that thegas should be led in contact with the cooled space in succession along aplurality of such machines. The capacities of the machines may be suchthat the gas to be cooled acquires the required temperature in a numberof suitably chosen steps, since this method has the advantage that, froma thermo-dynarnic point of view, the cooling process is thus performedfavourably and is therefore economical.

The machine may, for example, be constituted by an assembly of fourunits, in which the temperatures of the hot spaces generally be chosento be approximately equal, for example, equal to room temperature, but,if necessary, independently of one another. However, the temperatures ofthe cold spaces of all four machines are difierent. The gas to be cooledmay be led successively along the coolers of lower temperature.

What I claim is:

1. An apparatus for producing liquid air from gaseous air comprisingmeans for compressing said gas to at most 40 atmospheres, aheat-exchanger for cooling said gas, a cold-gas cooling machine forfurther cooling said gas and for forming a product including at least aliquid therein, said cold-gas cooling machine having twointercommunicating chambers of different temperatures, a medium ofinvariable chemical composition in said coldgas cooling machineconstantly in a gaseous phase and traversing in a cyclic process saidchambers, and means for reducing the pressure of said product.

2. An apparatus for producing liquid air from gaseous air comprisingmeans for compressing said gas to at most 40 atmospheres, a firstheat-exchanger for cooling said gas, a cold-gas cooling machine forfurther cooling said gas and for forming a product including at least aliquid therein, a second heat-exchanger for further cool ing saidproduct, said cold-gas cooling machine having two intercommunicatingchambers of different temperatures, a medium of invariable chemicalcomposition in said cold-gas cooling machine constantly in a gaseousphase and traversing in a cyclic process said chambers, and means forreducing the pressure of said product.

3. An apparatus producing liquid air from gaseous air comprising meansfor compressing said gas to at most 40 atmospheres, a heat-exchanger forcooling said gas, a cold-gas cooling machine for further cooling saidgas and for forming a product including at least a liquid therein, saidcold-gas cooling machine having two intercommunicating chambers ofdifferent temperatures, a medium of invariable chemical composition insaid coldgas cooling machine constantly in a gaseous phase andtraversing in a cyclic process said chambers, means for reducing thepressure of said product, and means for fractionating said product intoits components.

4. An apparatus for producing liquid air from gaseous air comprisingmeans for compressing said gas to at most 40 atmospheres, a reversibleregenerator for cooling said gas, a cold-gas machine for further coolingsaid gas and for forming a product including at least a liquid therein,said cold-gas cooling machine having two intercommunieating chambers ofdifferent temperatures, a medium of invariable chemical composition insaid cold-gas cooling machine constantly in a gaseous phase andtraversing in a cyclic process said chambers, and means for reducing thepressure of said product.

5. An apparatus for producing liquid air from gaseous air comprisingmeans for compressing said gas to at most 40 atmospheres, a firstheat-exchanger for cooling said gas, a cold-gas cooling machine forfurther cooling said gas and for forming a product including at least aliquid therein, a second heat exchanger for further cooling saidproduct, said cold-gas cooling machine having two intercommunicatingchambers of different temperatures, a medium of invariable chemicalcomposition in said coldgas cooling machine constantly in a gaseousphase and traversing in a cyclic process said chambers, means forreducing the pressure of said product, and means for fractionating saidproduct into its components.

References Cited in the file of this patent UNITED STATES PATENTS1,553,546 Lundgaard Sept. 15, 1925 1,901,389 Flamand Mar. 14, 19332,090,163 Twomey Aug. 17, 1937 2,105,214 DeBaufre Jan. 11, 19382,423,273 Van Nuys July 1, 1947 OTHER REFERENCES Separation of Gases, byRuhemann, published 1940, pp. 76 to 82 and and 161.

